(1) U.S. Pat. No. 7,174,223 B2, Dalton et al. (Cochlear) describes direct bonded wire feedthrough leads for cochlear implants including the bonding of Pt leads into alumina ceramics and co-firing. Column 1 in the Background describes inserting pins into a green ceramic plate and sintering. The method described is one where pins are inserted into holes in the ceramic. Holes can be drilled, punched, pressed, etc. The process is labor intensive, has low manufacturing yields and cannot achieve the close lead-to-lead spacing that is available with the present invention.
(2) U.S. Pat. No. 5,434,358, Glahn and Montesano describes examples of high Temperature Co-fired Ceramic (HTCC) processing, which are typically utilized in applications other than biomedical implants, and do not typically use materials that are considered to be biocompatible. Traditional HTCC processing typically involves screen printing of inks onto ceramic tape but would not include co-firing of wires or metallic forms and would not be used as an interface between electronics and human body fluids (or in batteries or capacitors) in an implantable device. HTCC uses molybdenum or tungsten (and potentially their alloys) as leads—these are not appropriate for implantable systems due to concerns about corrosion in body fluids. HTCC technology further relies on vias, which for the purpose of this document may be defined as leads that are perpendicular to the plane of the substrates which make up a feedthrough. Vias have limitations with regard to lead-to-lead spacing, and suffer from diminished integrity of the ceramic substrates resulting from holes being pierced in them to form vias.
(3) U.S. Pat. No. 6,586,675 B1, Bealka and Decosta (“the '675 patent”) describes brazed feedthroughs in which wire leads are brazed into metallized through holes using precious metal braze. These types of feedthroughs are appropriate where used, however issues of yield loss are associated with metallization and brazing of the lead seals. Metallization for the lead seals must extend beyond the lead, thereby increasing the size of the feedthrough and device.
(4) US patent application 2007/0217121 A1, Frysz et al. describes “integrated filter feedthrough assemblies made from low temperature co-fired (LTCC) tape” and relates to EMI filtering feedthroughs, and in general to construction of the capacitor itself.
(5) US patent application 2007/0060969 A1, Burdon et al. describes multilayer constructions with vias being “implantable co-fired electrical feedthroughs.” Burdon et al. describes feedthrough lead connections (“vias”) that are perpendicular to the direction of the ceramic tape or insulator layer. This type of construction is limited because the process of piercing the substrates and subsequently filling the vias is not reliable for producing a robust construction. Because of difficulties in the process of filling the via holes, hole-to-hole spacing cannot be reduced to the distances achieved in our invention. Some of their constructions show leads going through the ceramic not in straight paths, which is done to minimize the tendency of via feedthroughs to be non-hermetic. This approach consumes critical space within the feedthrough and thus the device. US patent applications 2007/0236861 and 2007/0060970 by the same authors are similar, and suffer from the same limitations due to the incorporation of vias. Note that paragraph 24 of 2007/0236861 states that the vias may be staggered through the substrates to improve integrity of the feedthrough—which in a roundabout way says that vias are not robust enough for the application without using up valuable space to offset the vias in a particular lead.
(6) Construction of high density feedthroughs for retinal prostheses are discussed in “Microelectronic retinal prosthesis: III. A new method for fabrication of high-density hermetic feedthroughs” by Suaning, G. J., Lavoie, P., Armitage, T., Forrester, J., Lovell, N. H., (2006), Proceedings of the 28th IEEE EMBS Annual International Conference, 30 Aug.-3 Sep., 2006, New York, USA. This method uses pre-sintered alumina substrates bonded together with alumina slip, and platinum metal traces. Very limited feedthrough geometries are available because of the use of fired substrates prior to bonding them together with leads. Fired substrates warp when re-fired, creating difficulties in closely matching and bonding the outer diameter of the feedthrough to inner diameter of the flange and hence difficulty in obtaining a hermetically sealed feedthrough. Our invention allows machining of the ceramic in unfired state, while this disclosure utilizes fired ceramic which is harder and more difficult to machine. Bonding fired substrates with slip is not very reliable as the slip will be constrained against shrinking in the plane of the substrates. Suaning et al. does not describe ink or wire patterns for forming leads as our invention does.
(7) US patent application 2008/0314502, Ok et al. “Method for Providing Hermetic Electrical Feedthrough” and US patent application 2006/0283624, Ok et al. “Method and Apparatus for Providing Hermetic Electrical Feedthrough” describe using vias of either ink or wire as leads running perpendicular to the plane of the ceramic substrate. The construction is similar to the multilayer constructions previously described, with the same limitations regarding center-to-center lead spacing and robustness of manufacturing process. The 2006/0283624 patent application is not essentially different than Dalton et al above, and the 2008/0314502 application seems very similar (with similar limitations) to the Burdon patents cited above in (5).
(8) U.S. Pat. No. 7,211,103 B2, Greenberg et al. describes a device that utilizes the feedthroughs from patents in (7) above, and suffer from the same limitations.
The entire contents of the documents identified in sections (1)-(8) above are incorporated herein by this reference.